Lubricants are used to reduce wear between moving parts where there is metal to metal contact and to remove heat from the parts. The lubricants typically contain a high viscosity base stock and a variety of additives to improve wear, friction coefficient, oxidation resistance and the like. Automotive gear applications are typically formulated for a base oil having a viscosity at 100° C. of about 30 cSt or more and a viscosity index of greater than about 80, known as Bright Stock. Such Bright Stock base oil is particularly suitable for gear applications due to its ability to remain clear and maintain suitable viscometric properties under extreme operating conditions. However, from time to time, the availability of Bright Stock base oils may become limited or the price may become excessive. Accordingly, there is a need for gear oil formulations that may be used to provide comparable or superior lubricating characteristics with a mixture of base oils containing base oil components having a viscosity of less than 30 cSt at 100° C. and a viscosity index of less than 80.
With regard to the foregoing, the disclosure provides a gear oil lubricant composition that includes a) a major amount of a base oil having a lubricating viscosity; b) a polysulfide extreme pressure agent; and c) a reaction product of an acylated copolymer and a polyamine.
In another embodiment there is provided a method for lubricating an automotive gear by providing a lubricant composition that includes a) a major amount of a base oil having a lubricating viscosity; b) a polysulfide extreme pressure agent; and c) a reaction product of an acylated copolymer and a polyamine.
A further embodiment of the disclosure provides a lubricant additive concentrate for a gear oil lubricant composition. The additive includes a) a polysulfide extreme pressure agent and b) a dispersant viscosity modifier that is a reaction product of an acylated copolymer and a polyamine.
In yet another embodiment there is provided a method of operating a vehicle containing a drive axle. The method includes providing as a lubricant for the drive axle a composition containing a) a base oil of lubricating viscosity, b) a polysulfide extreme pressure agent, and c) a dispersant viscosity modifier that is a reaction product of an acylated copolymer and a polyamine.
An advantage of compositions according to the disclosure is that a wider variety of base oils may be used to prepare the lubricant compositions for automotive gear applications. Accordingly, base oils that would not provide suitable thermal and oxidative stability and shear stability for automotive gear applications in the absence of the additive combination of the disclosure, may be used as total or partial replacement for Bright Stock base oils for such applications. Another advantage is that the lubricant compositions according to the disclosure may be formulated from commercially available components. The following detailed description of embodiments may provide other advantages.